Dojo Kun - literal translation means "training hall rules". There are five main rules that serve as guiding principles for all who train in the dojo. Although they are usually listed in a set order, no one rule is more important than any other. To emphasise this all five are prefixed with hitotsu and end with koto, which together mean "one point".
One Point! Seek Perfection of Character
Hitotsu! Jinkaku kansei ni tsutomuru koto
I urge you to research the meaning of the dojo kun and to draw your own conclusions as to the true meaning of each rule (start here at Wikipedia). Then, once you've done that, set upon Gichin Funakoshi's 20 Precepts (Niju Kun) and see what you make of them.
Here's my take on Seek Perfection of Character. The important word to stress here is "Seek", not find, obtain or acquire but Seek, as in "look for" or "search for". The inference being, you'll spend your whole lifetime in pursuit of this worthy goal but you probably won't find it. Using the paradox of Zen Wisdom to make sense out of nonsense, as human beings we are all imperfect and yet we are all perfect in and of ourselves at any particular point in our lives. We all do the best we can, with what we've got at any point in time. If you work on the premise of "good, better, best" at the end of each day we can say to ourselves, I did good today, tomorrow I'll do better, and eventually I'll find the best way. But that best way is way off in the distance. It could be argued that our characters are perfected at the moment we draw our last breath, because we cannot hope to seek any further from that point on, and if we cannot seek then we cannot possibly find what we have spent a lifetime looking for — perfection of character.
To illustrate the point of this being a life-long pursuit, the following extract comes from an article by renowned martial artist and author Dave Lowry entitled Not Yet, Not Yet from the February 1989 edition of Black Belt magazine.
In 1957, when Gichin Funakoshi was 89 years old and only a few months away from his death, he was speaking to some of his students about karate technique. Making a fist and rotating his elbow, Funakoshi performed soto ude uke, the outer forearm block. "I believe I might finally be beginning to understand this," he is supposed to have said.
Other sources have stated oi-tsuki as the technique in question, which is of little matter as the point is clear. That's a very basic technique the recognized father of modern-day karate was still "perfecting" at the age of 89. Whenever you get the opportunity to train with a master, don't be dismayed if you've paid a hefty seminar fee and all he does is go over the basics. Pay very close attention if this is the case. The devil is in the detail as they say. We can spend several years believing we are practicing a technique the right way only to find that we've been practicing the wrong way and it then takes a lifetime to correct.